CPjr's 2010 F150 won't engage 4x4. I have pretty much fired the parts cannon at it and it's acting weirder at every turn. Here's the problem - When you select 4x4 the 4x4 won't engage and the message center says "Check 4x4" with a wrench... it does not throw a code that I can find w/ code reader.

I jacked it up and turned the front wheels in 2wd; the cv shafts don't turn, engage 4x4 with the same result. I went up to the firewall vacuum solenoid and it appeared to be bad... no matter the switch position the vacuum was not interrupted, so we replaced it. Still same result. That convinced me the solenoid wasn't getting a signal to interrupt the vac.

So we pulled every fuse we could remotely link to the 4x4 system and they all were good... but now it's doing quirky stuff; for instance the vacuum solenoid may or may not engage at engine start, regardless of the 4x4 switch position. If you start it in 2wd and pull the vac lines to the hubs there may or may not be any, but as soon as you pull and reconnect the supply the solenoid opens and vac passes through. Can't get it to close on command for the life of us. I can maybe chalk that up to cheap $20 Dorman Chinese part.

Thinking the transfer case wasn't responding we also changed the electric engagement motor on the back of the transfer case, but I don't know for sure if that does any more than shift the box into low range.

Anyone been here?

Could be shift motor.

I replaced that and it didn't make any difference. However, I haven't taken it off and held in my hand to see if it responds to the dash switch, but the vacuum solenoid doesn't respond to the dash switch. I thought about the switch itself, but the truck knows we're TRYING to engage 4x4, so I presuming it's working.

If I hold the shift motor in my hand under the truck should it try move when he hits the switch? BTW, the notes that was tied to the shift motor specifically said DON'T DO THAT!!!!

wondering if you ever figured this one out.

I am having the exact same issue that you are having.

Yes , but it's hard to point to what definitively fixed it. It started working shortly after I posted this. But it did on it's own time, and not immediately after changing any one part. Honestly, I think it was that vacuum valve the whole time. I think that was the problem and it just took some repeated attempts to get it to engage from lack of use. We did change shift motor but the old one seemed to work fine on the bench.

I'd really concentrate on that vacuum valve. I think that is most commonly the culprit.

im having the same issue .. works very intermittently .. bench checked shift motor .. worked properly .. the solenoid and vac valve work, however the voltage to the solenoid never changes regardless of where the switch is positioned .. so the vacuum is never released .. my question is .. does the switch directly function the solenoid or is there something else in the circuit ..

I almost never use my 4x4 but will engage it in the neighborhood and slowly drive a half block every few months just to check it